With respect to heat treatment methods for quenching by cooling of a metal material that constitutes a treatment object after it has been heated, oil cooling systems and gas cooling systems have conventionally been used if high-speed cooling is required.
In the aforementioned oil cooling systems, cooling efficiency is excellent, but fine cooling control is almost impossible, and the treatment object tends to deform. On the other hand, in the gas cooling systems, cooling control by gas flow rate control or the like is easy, inhibiting deformation of the treatment object, but cooling efficiency is poor.
Patent Document 1 discloses a technology which seeks improvement in cooling controllability and cooling efficiency by disposing liquid nozzles and gas nozzles around the treatment object, supplying cooling liquid from the liquid nozzles in a manner of spray (so-called mist cooling), and supplying cooling gas from the gas nozzles.